1. Field of the Invention
This invention relates to communication connectors that are configured to compensate for offending crosstalk.
2. Discussion of the Known Art
Communication connectors that are configured to suppress or to compensate for crosstalk that originates from within a mating connector, are generally known. As defined herein, crosstalk arises when signals conducted over a first path, e.g., a pair of contact wires in a communication plug connector, are partly coupled electromagnetically into a second signal path (e.g., another pair of contact wires) within the same connector. The signals coupled from the first path may be detected as xe2x80x9ccrosstalkxe2x80x9d in the second path, and such crosstalk degrades existing signals that are being routed over the second path.
Applicable industry standards for rating connector crosstalk performance are given in terms of near-end crosstalk (NEXT) and far-end crosstalk (FEXT). The ratings are usually specified for mated plug and jack combinations, and input terminals of the plug connector may be used as a reference plane. NEXT is defined as crosstalk whose power travels in an opposite direction to that of an originating, disturbing signal in a different path. FEXT is defined as crosstalk whose power travels in the same direction as the disturbing signal in the different path. See, e.g., xe2x80x9cTransmission Systems For Communicationsxe2x80x9d, Bell Telephone Laboratories (5th ed. 1982), at page 130. Communication links using unshielded twisted pairs (UTP) of copper wire are now expected to meet industry xe2x80x9cCategory 6xe2x80x9d standards which call for at least 54 dB NEXT loss and 43 dB FEXT loss, each at 100 MHz, with respect to any two signal paths through the mated connectors.
Crosstalk compensation circuitry may be provided on or within layers of a printed wire board to which the contact wires of a communication jack are connected. See U.S. Pat. No. 5,997,358 (Dec. 7, 1999), all relevant portions of which are incorporated by reference. U.S. Pat. No. 6,139,371 (Oct. 31, 2000), also incorporated by reference, relates to a communication connector assembly having capacitive crosstalk compensation. The assembly features a number of terminal contact wires at least first and second pairs of which have free end portions that extend to define leading portions. A leading portion of a first pair of contact wires, and a leading portion of a second pair of contact wires, are dimensioned and arranged for capacitively coupling to one another so as to produce capacitive crosstalk compensation. See also commonly owned U.S. application Ser. No. 09/583,503, filed May 31, 2000, and entitled xe2x80x9cCommunication Connector with Crosstalk Compensationxe2x80x9d, and U.S. Pat. No. 5,700,167 (Dec. 23, 1997) which discloses inductive crosstalk compensation circuitry in the form of conductive loops that are printed in mutual coupling relation on a printed wire board.
It is also known that in conventional modular communication plugs, capacitively coupled and inductively coupled signal components add for NEXT, while they subtract for FEXT. That is:
NEXT=Xc+Xm
and
FEXT=Xcxe2x88x92Xm,
wherein:
Xc is the capacitively coupled component, and
Xm is the inductively coupled component.
It is also known that the effectiveness of any NEXT cancellation scheme is limited by the amount of delay between the offending crosstalk and the compensating crosstalk, and that NEXT cancellation may be improved by reducing such delay with optimum cancellation occurring when the delay is effectively zero. The connector configuration in the mentioned U.S. Pat. No. 6,139,371 minimizes the delay for capacitive crosstalk compensation by deploying the capacitive compensation coupling at non-current carrying free ends of the contact wires in a modular jack, effectively at the connection interface where the offending crosstalk is introduced by the mating plug.
If all existing NEXT is compensated using capacitive coupling at the non-current carrying wire free ends, NEXT would be effectively canceled because delay is minimized. But FEXT performance may be degraded, however, since the compensation being provided is totally capacitive in nature.
Further, if a configuration such as in the ""371 patent is used only to cancel the capacitive component of the original crosstalk, and inductive coupling is also provided to compensate for the offending inductive component (see, e.g., U.S. Pat. No. 6,196,880 issued Mar. 16, 2001), FEXT would be minimized but the efficiency of NEXT cancellation may be reduced due to a time delay caused by the remote placement of the inductive compensation which is effectively distributed over the length of the inductive coupling region. Thus, the need to maintain adequately low FEXT levels has been a constraint on the degree to which NEXT levels can be reduced.
According to the invention, a method of compensating for near-end and far-end crosstalk in a communication connector, includes producing capacitive compensation coupling at a first stage in. the connector wherein the capacitive compensation coupling corresponds in magnitude to a sum of offending capacitive crosstalk and offending inductive crosstalk both of which originate from a mating connector, and producing, at a second stage, both (a) inductive compensation coupling corresponding in magnitude to the offending inductive crosstalk from the mating connector, and (b) capacitive coupling corresponding in magnitude and of a polarity opposite to that of the inductive compensation coupling.
For a better understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawing and the appended claims.